(1) Field of the Invention
This invention is related to the conversion of hydrocarbon streams using a catalytic reforming catalyst having a modified pore size distribution and a reforming process using this catalyst.
(2) General Background
The reforming of hydrocarbon naphtha streams is an important petroleum refining process providing high octane hydrocarbon blending components for gasoline or for chemical processing feedstocks.
Catalytic reforming of naphthas can be carried out with several types of catalysts and in fixed or moving bed processes. Catalysts used in reforming processes generally contain a hydrogenation metal, typically a platinum group metal, to effect the conversion of the hydrocarbon naphtha feedstock to a product having increased value.
In the manufacture of reforming catalysts, many factors are considered to optimize the volume of high octane materials produced with a particular catalyst. In addition to varying the types and content of metals on the reforming catalyst base, modification of the physical properties of the catalyst base effect the catalyst's catalytic properties.
The primary physical properties of a catalyst base which can be changed during manufacture are surface area, pore volume and the distribution of pore sizes within the pore volume.
U.S. Pat. No. 4,082,697, Tamm, recognizes the need to modify the pore volume distribution of a reforming catalyst support to improve the catalytic properties of the finished catalyst. In particular, this patent discloses a specified pore volume of at least 0.5 cc/gram with at least 70 percent of the pore volume having pore diameters of from about 80 to 150 angstroms. Additionally, the pores having diameters greater than about 1,000 angstroms, according to the teachings of this patent, must be less than about 3 percent of the pore volume of the catalyst.
U.S. Pat. No. 4,104,153, Erickson, discloses a catalytic reforming catalyst in which alumina particles making up the catalyst support have a crystallite size of less than 100 angstroms which contributes to an increased porosity of the catalyst support and ultimately to improve catalytic properties of this catalyst. There is a general recognition that pore volume has an effect on the catalytic performance of the catalyst.
U.S. Pat. Nos. 4,036,784, Gembecki et al., and 4,124,537, Gembecki et al., both relate to the production of catalytic composite materials in which finished catalysts are produced by extruding an alumina which may contain catalytic hydrogenation metals. According to these patents, co-extrusion of the catalytic metals and the base material results in enhanced hydrodesulfurization catalyst activity when processing a vacuum gas oil feedstock.
U.S. Pat. No. 4,216,123, Banks et al., relates to catalysts for steam reforming of hydrocarbons and recognizes that a certain distribution of pore volume has a beneficial effect on catalyst activity.
Applicants have found that in modifying and controlling the pore volume distribution of a naphtha reforming catalyst base, increased catalytic activity can result when (1) surface area of the reforming catalyst is at least 250 square meters per gram, (2) the pore volume in pores having diameters of from about 30 to about 38,000 angstroms is greater than about 0.4, and (3) about 70 percent or less of the above pore volume is in pores having diameters of from about 30 to about 400 angstroms and about 30 percent or more of said pore volume is in pores having diameters of from about 400 to about 38,000 angstroms.
In particular, when the pore volume distribution of an experimental reforming catalyst had its base properties modified as described above, it showed a large increase in activity when compared to a prior art commercially used catalyst having a similar composition except for the catalyst base properties. There were additional catalytic effects which depended on the particular stage of catalyst manufacture when catalytic metals were placed on the experimental catalyst (e.g., before extrusion of the catalyst base or after extrusion of the base). The selectivity of the claimed catalyst for producing high octane C.sub.5 + materials was generally equal to the prior art catalyst.
The modified pore volume distribution is thought to result from (1) initially working or densifying the support (e.g., mulling) prior to extrusion, or (2) calcining the extrudate at a controlled relatively low temperature of from about 800.degree. F. to about 1200.degree. F., or (3) the use of PHF type alumina (e.g. spray dried, high purity alumina produced from a gelled sol) or combinations of the above.
Applicants' invention described herein, therefore, presents an advance in the art by providing a naphtha reforming catalyst having improved activity and can beneficially be used in the refining industry for producing higher quality gasolines or chemical processing feedstocks.